Below is a procedure I used to get a DS3231 RTC working last year. Not sure what chipset your RTC is using. I would assume it would need a driver loaded using a configuration similar to this. Unfortunately, the time architecture in the Pi appears to get further development and users are left to discover how to get it working once again.

Using your favourite text editor, add a call for the kernel to support a RTC on boot to the bottom of the /boot/config.txt file – a reboot is required for this change to take effect:

#enable RTC DS3231

dtoverlay=i2c-rtc,ds3231

Now that we have a time reference, let’s remove the two software packages that Raspbian uses for supporting time. From the command line interface (CLI), issue the following command to remove the NTP and fake hardware clock software:

sudo apt-get purge ntp fake-hwclock

Using the CLI, let’s establish the time zone configuration by entering the following command and following the prompts.

sudo dpkg-reconfigure tzdata

Now let’s establish the date and time. This can be done through the command line using the sudo date --set ‘yyyy-mm-dd hh:mm:ss’ command. That requires a little more typing than needed, so while the device is connected to a network, we’ll cheat and use an online time source to nail up the date and time.

sudo apt-get install ntpdate

sudo ntpdate <replace with the URL or IP address of a time source, this includes the parenthesis>